1. Field of the Invention
This invention relates to a plasticizer for chloroprene rubber. More particularly, it relates to a plasticizer for chloroprene rubber which comprises an ester of a glycol having a thioether bond with aliphatic monocarboxylic acid(s).
2. Description of the Prior Art
Chloroprene rubber, which is excellent not only in general physical properties of a rubber but also in various properties such as weather resistance, chemical resistance and flame resistance, has been widely applied to, for example, industrial products, building gaskets, high-way joint seals, automotive parts, electrical cables and adhesives.
However the ozone resistance and cold resistance of the chloroprene rubber are unsatisfactory. Thus it has been required to improve these properties thereof.
Similar to other commonly employed rubbers, chloroprene rubber contains plasticizers such as process oil or various ester oils. It is known that ester plasticizers such as unsaturated vegetable oils, butyl oleate or dioctyl sebacate improve the cold resistance of chloroprene rubber.
However none of these plasticizers can exert any satisfactory effect. Therefore there has been proposed to improve the cold resistance of chloroprene rubber by, for example, using an unsaturated carboxylic acid ester of a glycol (cf. Japanese Patent Laid-Open No. 122532/1984) or by employing a dibasic acid ester of an ether alcohol as a plasticizer therefor (cf. Japanese Patent Publication No. 44695/1979).
Although the cold resistance of chloroprene rubber can be improved to a certain extent by using these plasticizers, each of these plasticizers has an insufficient heat resistance, causes a significant physical change upon prolonged heating and shows a considerably poor ozone resistance. Thus these plasticizers are unsatisfactory from the practical viewpoint.